This invention relates generally to light load fastening devices, and more specifically to a fastening system employing a tubular eyelet pressed into a non-circular aperture in a rigid support plate for providing a predictable holding force in accordance with the number of contact points between the tubular eyelet and the non-circular aperture in the support plate.
It is well known in the fastening art to employ an eyelet which comprises a tubular metal shank with a head flange at one end as a fastening device. With such conventional eyelets the tubular shank is inserted through a hole in a workpiece and then set by outwardly flanging the end of the shank opposite the head flange. The length of the shank of such eyelets must be sufficient to pass completely through all of the parts of the workpiece being fastened together and project far enough from the workpiece to enable the eyelet shank to be set by outwardly flanging its tail end. Setting of such eyelets in conventional eyeletting machinery has become unreliable due to the eyelet shank collapsing within the thickness of the workpiece under the load imposed axially on the eyelet by the eyelet setting machinery. Also, this flanging operation causes spring back of the eyelet that is not predictable and consequently allows an indeterminable and undesirable loosening between the workpieces being fastened together. Besides, a flange may be undesirable for low profile designs or in applications which require a flat surface without protrusions.
Furthermore, any secondary operation such as outward flanging the tail end of the eyelet, adds to the complexity, time, and cost of fastening workpieces together. Also, the workpiece parts to be fastened together must be accessible from both sides in order to outwardly flange the tail end of the eyelet.
Other prior art fasteners include resiliently compressible shank portions which are typically barrel-shaped. Such fasteners are intended for use in circular apertures of slightly smaller cross sectional dimensions than an enlarged area of the resiliently compressible shank. Then, as the shank is forced into the circular aperture, it is compressed and its resilience provides a grip on the rim of the aperture that it extends through. While resilient shank fasteners need only be accessible from one side, their specialized and atypical design has made them prohibitively expensive for widespread commercial application. Furthermore, unless such resiliently compressible shanks are barrel-shaped and extend a significant distance through the workpiece, they do not provide reliable fastening. Still other fasteners having cylindrical shanks of resilient material provide a gripping bulge on the blind side of the workpiece when pressed into a circular aperture. These fastening systems depend on extremely tight tolerances of both the fastener and the aperture formed to receive the fastener. Consequently, widespread use of such fasteners is prohibitively expensive.
In the assembly of various devices, it is often desirable to provide a predictable predetermined holding force when fastening various members of the assembly together. For example, in the assembly of electronic devices, it is often desirable to provide a dust seal between switch housing components for preventing contamination of the switch contacts contained therein. To this end a compressible sealing member may be sandwiched between the housing components when fastening them together. If a fastener is employed that provides too light of a holding force, then a good seal is not created. On the other hand, if the fastener provides a holding force in excess of the compression of the compressible sealing member, the resulting distortion of the sealing member causes a poor seal to be created and may even damage or distort the parts being assembled causing expensive assemblies to be ruined. Before the present invention, there has been no simple fastener that would provide a predictable predetermined holding force. Therefore, it has not been previously possible to fasten components together with the holding force of the fastener reliably matched to the compression of the sealing member with an inexpensive fastening system.